Elevational dynamics in soil microbial co-occurrence: Disentangling biotic and abiotic influences on bacterial and fungal networks on Mt. Seorak

Fungi outperformed bacterial in maintaining the microbial co-occurrence networks. Fungi showed different elevational network co-occurrence pattern from bacteria. Distinct biotic/abiotic factors influenced bacterial and fungal network dynamics. The interplay between soil micro-organisms in mountain ecosystems critically influences soil biogeochemical cycles and ecosystem processes. However, factors affecting the co-occurrence patterns of soil microbial communities remain unclear. In an attempt to understand how these patterns shift with elevation and identify the key explanatory factors underpinning these changes, we studied soil bacterial and fungal co-occurrence networks on Mt. Seorak, Republic of Korea. Amplicon sequencing was used to target the 16S rRNA gene and ITS2 region for bacteria and fungi, respectively. In contrast to bacteria, we found that fungi were predominantly situated in the core positions of the network, with significantly weakened co-occurrence with increasing elevation. The different co-occurrence patterns of fungal and bacterial communities could be resulted from their distinct responses to various environments. Both abiotic and biotic factors contributed significantly to shaping co-occurrence networks of bacterial and fungal communities. Fungal richness, bacterial community composition (indicated by PCoA1), and soil pH were the predominant factors influencing the variation in the entire microbial co-occurrence network. Biotic factors, such as the composition and diversity of bacterial communities, significantly influenced bacterial co-occurrence networks. External biotic and abiotic factors, including climatic and vegetative conditions, had a significant influence on fungal co-occurrence networks. These findings enhance our understanding of soil microbiota co-occurrences and deepen our knowledge of soil microbiota responses to climatic changes across elevational gradients in mountain ecosystems.